Rock-drill having an engine assembled therewith



July 20, 1954 G. A. BERGMAN 2,684,055

ROCK-DRILL HAVING AN ENGINE ASSEMBLED THEREWITH Filed Feb. 25, 1952Enventor:

(Ittornegs.

back in a return stroke.

Patented July 20, 1954 ROCK-DRILL HAVING AN ENGINE ASSEM- BLED THEREWITHGustav Albert Bergman, Danderyd, Sweden Application February 25, 1952,Serial No. 273,240

In rock-drills and similar motor-driven tools provided with an impactpiston operated by means of an internal combustion engine assembled withthe rock-drill, the impact piston forms a movable wall in the enginecylinder or, in other words, a movable cylinder head at one end of theengine cylinder. The impact piston receives its reciprocating motion bythe fact that the pressure from the gases of combustion drives it, uponevery ignition in the engine cylinder, outwardly in a working stroke,compressed gases on the outside of the impact piston then driving it Thecompressed gases are inclosed within a cylinder space on the outside ofthe impact piston, and this device is designated in the following as agas cushion. In a known construction, the inlet of the gas cushion is inopen communication with a source of compressed gas, and is provided withan outlet which is open toward a channel leading through the boring tooldown into the bore-hole, wherein the tool operates, the escaping gasesbeing utilized for the scavenging of the bore-hole. In this connection,certain losses come about by the fact that gas is pressed from thecylinder of the impact piston back through the inlet passage during theWorking stroke of the impact piston, while gas escapes at the same timethrough the outlet from this cylinder. In certain cases, the

losses become so large that a sufficient pressure will not be attainedon the outside of the impact piston for the return movement of thepiston. This manifests itself by the impact piston operating too slowlyand by the impact efiect becoming low. The rate at which the boring toolworks itself down into the bore-hole will be small in a correspondingdegree.

The object of the present invention is primarily to obviate thesedisadvantages and to attain a rapid movement of the impact piston and acorrespondingly high boring rate. The substantially distinguishingfeature of the invention resides above all in that the inlet to the gascushion has provided therein a non-return valve closing at a dischargefrom the gas cushion. A powerloaded, preferably spring-loaded valve mayalso be arranged in the outlet from the gas cushion, said valve beingadapted to be opened for the discharge of gas from the gas cushion onlyat the attainment of a certain pressure in the latter. If the inletopens into the cylinder of the impact piston at the bottom of thecylinder, the

4 Claims. (Cl. 123-7) non-return valve prevents a return flow fromimpact piston, and at the same time the powerloaded valve in the outletensures that the pressure of the gas cushion falls below a certainsuitable value. Hereby the return movement of the impact piston becomessafer and quicker.

Generally, the engine cylinder proper is used as a source of gaspressure, the inlet channel of the cylinder of the impact piston thencommunicating with this cylinder of the engine. It is also possible,however, to make use of a special compressor operating with air, forexample, said compressor delivering the requisite pressure medium to thegas cushion, while the non-return valve is arranged in the communicatingpassage between the compressor and the gas cushion.

An example of the application of the invention is illustrated in theaccompanying drawing. Fig. 1 shows the rock-drill, partly in axialsection. Fig. 2 shows, to a larger scale, the nonreturn valve in theinlet of the cylinder of the impact piston, and Fig. 3 shows, likewiseto a larger scale, the power-loaded valve in the outlet.

In the drawing, i designates the cylinder of the internal combustionengine, 2 the operating piston thereof, and 3 the combustion chamber. 4

denotes the impact piston and 5 the cylinder of the impact piston. Theimpact piston is provided with an auxiliary piston ii of a largerdiameter, and this auxiliary piston moves in an enlarged end portion ofthe impact piston cylinder. The cylinder space I on the outside of theauxiliary piston '5 encloses the gas cushion. This gas cushioncommunicates through a passage 8 with the combustion space 3.Furthermore, the

gas cushion communicates through an outlet passage 9 with an annularspace it, which is connected, through the intermediary of grooves ii inthe impact piston rod it, with the interior of a sleeve i l serving asan attachment for the boring tool l5. Leading through the boring tool isan axial passage l6 reaching down to the operating end of the tool, sothat gases entering the sleeve M through said passage may be conveyeddown into the bore-hole.

According to the invention, a non-return valve is arranged in the inletpassage, said non-return valve closing at an escape of fluid from thegas cushion 7. According to the drawing, the nonreturn valve takes theform of a ball ll cooperating with a seat 58 in a recess E9 in thebottom of the impact piston cylinder. The channel 8 opens from belowinto the bottom of the recess l9, and immediately above the valve ball11, a plate 20 or the like is secured in the bottom of the cylinder,said plate partly preventing the ball ll from being thrown up from therecess, and partly guiding the hot gases rushing out of the inlet 8toward the sides, so that they are prevented from meeting the auxiliarypiston 6. The recess Hi extends laterally approximately on a chord ofthe cylinder bottom, and the bottom 2| the recess slopes obliquelyupwardly toward the cylinder bottom to merge by degrees into the latter,as shown in Fig. 2.

According to the invention, the outlet passage 9 also has a power-loadedvalve arranged therein, said valve opening only at the attainment of acertain pressure in the gas cushion. This valve may consist of a valveball 22 cooperating with a seat 23 formed by the bottom of a recess 24in the cylinder chamber 21 of the impact piston. The recess 24 is closedat the top by means of a screw stopper 25, which keeps a spring 2% inthe recess against the valve ball. The latter is thus loaded by acertaindefinite force, which may be controlled, if desired, by the screwstopper being screwed in more or less.

The passage 9 commences with an opening 21 in the cylinder wall at adistance above the bottom of the impact piston cylinder, by reason ofwhich it will be cut oil by the auxiliary piston 6 during the outwardmovement of the latter (downwardly in the figure) The mode of operationof the machine described is broadly as follows. At the ignition and theimmediately following combustion in the engine cylinder 3, the impactpiston 4 will be thrown with its auxiliary piston 5 in a direction outfrom the combustion chamber 3 by the pressure then produced. Gas willthus be compressed on the lower side of the auxiliary piston 6 in thecylinder space '2. When a certain pressure has been produced in thelatter, before the auxiliary piston has reached the opening 21 of theoutlet passage d, the force of the spring 26 acting upon the valve ball22 may be overcome, so that the valve ball will be raised from the seat23 so as to admit the gases into the passage 9. These gases continue tothe annular space it through the slots I l to the sleeve l4 and throughthe axial channel it in the boring tool l5 down into the bore-hole toscavenge the latter clean from boring-dust and the like produced duringthe boring work. However, before the impact piston has had time to moveappreciably, the gases of combustion, which are under a high pressure,have been permitted partly to flow through the channel 8 past thenon-return valve l1 into the cylinder space i. After the impact pistonhas moved for a distance, it covers the opening 2! of the outer passage9, whereupon the pressure in the cylinder space 7 rises rapidly. When itexceeds the pressure of the inlet passage 8, the non-return valve llcloses, whereupon the gas cushion in the space 7 is cut off both on theinlet side and on the outlet side. For this reason the auxiliary pistoncannot reach the bottom but will rebound against the gas cushion intothe inner end position shown. The procedure is then repeated anew at thenext combustion in the engine cylinder.

Although the invention has been described as applied to rock-drills withboring tools, it obviously also comprises similar machines with othertools, such as breaking tools, chisels, harnmers and the like. Nor isthe invention otherwise limited. to the construction shown, which onlyaims at illustrating an example of em- .bodiment,

What I claim is:

1. In a rock drill driven by an internal combustion engine by impact, acylinder, a conduit connecting the combustion chamber of said combustionengine with said cylinder, an impact piston movable in the cylinder anddefining a gas chamber to form a gas cushion in the cylinder forreturning the impact piston, a non-return valve in said conduit openingtoward said cylinder chamber to permit introduction of combustion gasesfrom the combustion chamber of the engine into said gas chamber butpreventing return of the gases.

2. In a rock drill driven b an internal combustion engine, a cylinder,an impact piston movable in said cylinder and defining a gas chamber toform a gas cushion at the impact side of the piston for the returnstroke of the impact piston, said cylinder having an inlet for gas underpressure and an outlet for gases, and a spring-loaded valve in saidoutlet opening outward from the cylinder.

In a rock drill driven by an internal combustion engine, a cylinderhaving an outlet, a passage for gas forming a communication between thecombustion chamber of the combustion engine and said cylinder, an impactpiston movable in the cylinder and defining a gas chamber in thecylinder to form a gas cushion for the return of the impact piston, anon-return valve in said passag opening toward the cylinder chamber, anda spring-loaded valve in the outlet adapted to open outward from thecylinder chamber at a predetermined gas pressure therein.

4. In the rock drill claimed in claim 3, a through passage in the toolof the rock drill, the spring loaded valve being mounted in saidpassage.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,920,765 Rasch Aug. 1, 1933

